The present invention relates to image processing and, more particularly, to an automatic method for correcting the contrast and intensity of color still and video images.
The perceived colors of visible objects are determined, both by the physics of light reflection and by the way in which the visual system processes the reflected light that it receives. With regard to the physics, the physical color of the light reflected to the visual system by visible objects is determined, both by the reflectivity spectra of their surfaces, and by the color spectrum of the illuminating light. Photographs of scenes, including both still pictures and motion (e.g. video) pictures, whether recorded by analog means (photographic film) or digital means (video cameras), normally are perceived differently from the way the scenes themselves would be perceived by direct vision.
Most prior art methods dealing with color image processing of still and video pictures, and specifically with color and intensity contrast, approach the subject of improving or adjusting such contrast and/or intensity using principles unrelated to the human visual system and its physiology. A previous patent awarded to one of the present co-inventors, U.S. Pat. No. 5,771,312, describes physiologically-based color constancy adjustment of pictures, but does not deal with either color or intensity contrast. We are not aware of any method similar to the one proposed herein, that aims to emulate the human vision for improving color contrast and intensity. Present color contrast adjustment methods thus lack many of the physiological-like features that can lead to much improved color pictures.
There is thus a widely recognized need for, and it would be highly advantageous to have, a satisfactory method for performing color contrast correction, either automatically or interactively, on both still and video (motion) pictures. There is also a widely recognized need for, and it would be highly advantageous to have, a satisfactory method for performing local intensity correction, either automatically or interactively, on both still and video pictures.